The wireless monitoring of vital signs is particularly important for remote health monitoring. This allows patients and consumers to monitor their health with greater flexibility than traditional wired approaches. Recently, with the advent of Bluetooth technology, and in particular, Bluetooth Low Energy (BLE), remote sensing has gained more capabilities. This allows devices to be paired with apps on smartphones. These basic technologies have inspired the new wave of wearables for health and fitness. There does not exist, however, a comprehensive technology that measures important medical vital signs in a continuous manner. Most approaches fail to measure one or more of the important vital signs.
EKG is conventionally measured by the use of 12-lead systems in the hospital. For portability, the Holter monitor is utilized to capture cardiac events over the course of an extended time period. Unfortunately, this approach is difficult because it requires the attachment of wires to various parts of the body and then a sizable battery-powered unit that is worn on the belt. After a certain time period of recording, data is transmitted over the telephone. This method is still in use today and is a means to capture cardiac events from patients. The size and weight of the unit makes it cumbersome for most users.
Measurement of pulse oximetry is done using a finger probe. The probes shine a red light and an infrared light through the finger and then measures the change in absorbance from beat-to-beat. The relative ratio of the absorbance is presented as the ratio of ratios, the ratio of the AC signal of red over the DC signal of red over the AC signal of infrared over the DC signal of infrared. This ratio method corrects for any DC drift in the system and allows the ratios of the two wavelengths to be measured accurately. At 660 nm, deoxygenated hemoglobin Hb absorbs more than oxygenated hemoglobin HbO2. At 910 nm infrared, the HbO2 absorbs more than the Hb. The finger probes can be worn briefly, but interfere with daily life and tasks.
It is easy to measure skin temperature in a continuous manner or to measure core temperature in a single measurement. However, continuous core body temperature measurement is challenging. This would require an internal probe in the gastrointestinal tract, a catheter, or some other internal probe. These are invasive and cannot be utilized in routine settings for consumers and patients. Core body temperature fluctuations can happen quickly, signaling worsening infection or some other process that needs medical attention fast.
Heart rate and respiratory rate are important physiological parameters that give significant insight into health and wellness. Heart rate is readily derived from both photoplethysmograph (PPG) and EKG signals. Weak EKG or PPG signals can lead to inaccuracies and ideally, the heart rate and respiratory rates can be redundantly analyzed from both data traces.
Blood pressure measurements are currently performed utilizing cuff-based approaches, typically a sphygmomanometer that is applied around the arm. Inflation of the cuff using a rubber bulb occludes blood flow allowing for determination of blood pressure. Both the systolic and diastolic blood pressures can be determined by listening to the Korotkoff sounds generated during this process. The sounds are heard using a stethoscope and interpreted by a skilled medical professional. This approach gives only individual and not continuous blood pressure readings.
There are significant challenges that need to be overcome in order to have continuous measurement of core vital signs, especially in a small, low power form factor.